Sign up via socials

Hi, I develop an Angular5 application and want to use Auth0 authentication.
I need Sign up users via socials like Google, Facebook, Twitter.
I want to use my custom Sign in/Sign up form.
I developed custom Sign in/Sign up via email and password. Sign in via socials developed successfully.

But I don’t understand how can I realize Sign up functionality via socials networks, I can’t find methods for Sign up via socials.
Also, I need to check does user exists in the database at moment of Sign up via socials.

There is no real distinction between a user signing in and a user signing up in the context of social connections. Auth0 will create a profile for the social login if it’s not already present, but other than that there is no distinction.

If you need to check the presence of a user you can use the management API to search for the email address. If a profile is found, you can check the identities array to see which social identities are linked to the user.